Despite the international flavor, ORNL is less welcoming to foreigners than universities and even some of the other national labs, such as Argonne in Illinois and Lawrence Berkeley in California, Pennycook said. That's because they don't have the same security concerns as Oak Ridge, he said.

Most Oak Ridge facilities are dedicated to open science. That includes a powerful stable of supercomputers, featuring the Cray XT5 "Jaguar" - currently the fastest machine in the world. But about a hundred yards from the computing center is another modern, three-story brick building that houses the lab's national security program, which includes classified projects for the military and intelligence agencies, and it's strictly off-limits to foreign nationals.

"We work pretty hard to keep things separate," said Mason, who became ORNL director in 2007, barely a year after becoming a U.S. citizen. "We don't want the open, international world to get into our national security space. We also need to make sure that the national security way of doing things doesn't impede our ability to be players in science in the world."

I'm guessing that the security concerns are similar at Los Alamos, Sandia, and Lawrence Livermore labs.